It has heretofore been known that, in an electric vehicle such as an electric automobile or a hybrid car equipped with a motor, an inverter and a motor control unit are provided between the motor and a power supply unit, and a motor current which is a driving signal is sent to the motor by the inverter to drive the motor. The inverter converts DC power from the power supply unit into an alternating current in accordance with a torque command value, and sends the resultant motor current to the motor. Further, the motor control unit sends, to the inverter, a control signal for generating the motor current.
As one such electric vehicle, there has heretofore been a hybrid vehicle including a control unit, and a first motor generator (MG1) and a second motor generator (MG2) which are two motors connected to two inverters, respectively. Some such hybrid vehicles have been configured to perform a so-called “ready-off”. In a ready-off, the control unit stops the driving of both of the two motor generators to decrease a motor load factor when an overcurrent is generated in one of the inverters, and, after the overcurrent has disappeared, the control unit resumes driving of both of the inverters. Afterward, when an overcurrent is generated again, the control unit again stops driving both the inverters to further decrease the motor load factor. This operation may be repeated, for example, four times. After four repetitions, the control unit stops the driving of both inverters. Here, “motor load factor” refers to the ratio of an allowable maximum torque command value of the motor to a generatable maximum torque of the motor. Therefore, a decrease in the motor load factor corresponds to a decrease in the overall driving force of the vehicle.
Furthermore, Japanese Patent Publication Laid-open No. 2004-112883 describes a hybrid car including a control unit and two inverters which are connected in parallel to a DC power source and to two motors, AC motors M1, M2. When one of the two inverters abnormally stops, the control unit forces the other inverter to also stop. Moreover, after having compulsorily stopped the second inverter, the control unit releases that inverter from the forced stop when the level of a voltage output from a voltage sensor is stabile after a predetermined period of time.
The conventional hybrid vehicle described above includes the two inverters, the first motor generator (MG1) and the second motor generator (MG2), and the control unit. The control unit stops the driving of both of the two motor generators to decrease the motor load factor when an overcurrent is generated in one of the inverters. Moreover, after the overcurrent has disappeared, the control unit resumes the driving of both of the inverters. Subsequently, should overcurrent reoccur, the control unit again stops driving both the inverters to decrease the motor load factor. This operation is continuously repeated. Because the generation of the overcurrent is successively repeated in the inverter when one of the inverters is broken, the motor load factor might gradually decrease even if the driving of the inverters is resumed, until, ultimately, sufficient running performance of the vehicle might not be obtained. For example, the motor load factor might decrease to such a degree that sufficient acceleration force is not obtained, or neither of the two motor generators might be driven. Therefore, when the overcurrent is generated in the inverter, a driver might only be able to coast the vehicle, even if the driver only attempts to drive the vehicle to the side of a road or to, for example, an automobile repair shop. Accordingly, there remained a need to enable effective safe driving for evacuation.
Furthermore, the hybrid car described in Japanese Patent Publication Laid-open No. 2004-112883 does not include unit for selecting an inverter to be driven when an overcurrent is generated in an inverter, and for controlling the inverter to only drive the selected one of the plurality of inverters so that the motor corresponding to the selected inverter may be driven, and wheels are driven by the motor corresponding to the selected inverter when the overcurrent is generated in one of the inverters. The hybrid car described in Japanese Patent Publication Laid-open No. 2004-112883 therefore there is room for improvement to enable effective safe driving for evacuation to the side of a road or to, for example, an automobile repair shop when the overcurrent is generated in one of the plurality of inverters.